Embolism of cardiac origin accounts for about 1/4 of ischemic strokes. Strokes due to cardioembolism are in general severe and prone to early and long-term recurrence. Cardioembolism can be reliably suspected in clinical grounds but is often difficult to document. Magnetic resonance imaging, transcranial Doppler, echocardiogram, Holter and electrophysiological studies can help to demonstrate the source of cardioembolism. Aortic arch atheroma is an emerging embolic source, but non-valvular atrial fibrillation remains the commonest cause of cardioembolic stroke. Despite its preventive potential, continuous oral anticoagulation is prescribed for less than half of the patients with atrial fibrillation with risk factors for embolism and no contraindications for anticoagulation. The embolic risk of patent foramen ovale is low except when combined with an atrial septal aneurysm. Available evidence does not support routine immediate anticoagulation of acute cardioembolic stroke.